Communication system



Aug. l0, 1943.

R. H. CAMPBELL COMMUNICATION SYSTEM Filed Jan. 16, 1942 4 Sheets-Sheet 1 wwwa@ gg Aug 10, 1943- R. H. CAMPBELL 2,326,616

COMMUNICATION SYSTEM Filed Jan. 16, 1942 4 Sheets-Sheet 2 l 57,1 rfa/v 5 57A T10/v 7 ug. 10, 1943. R, H CAMPBELL 2,326,616

COMMUNICATION SYSTEM Allg. 10, `1943. R H. CAMPBELL 2,326,616

COMMUNICATION SYSTEM Filed Jan. 16, 1942 4 Sheets-Sheet 4 I 166.2 {zal/.2 WSLZ I J J i Patented Aug. l0, 1943 COMMUNICATION SYSTEM Richard 1I. Campbell, Racine, Wis., assignor to Webster Electric Com poration of Delaware pany, Racine, Wis., a cor- Application January 16, 1942, Serial No. 426,978

26 Claims.

The present invention relates to communication systems and more particularly to intercommunicating systems of the loudspeaking type.

Different requirements in various installations have resulted in the development of a number or types of intercommunicating systems. Probably the simplest type is a system comprising a central or master station and a number of substations, the former being provided with an ampiier, a loudspeaker adapted to be utilized also as a microphone, a station selector switch or switches, and a communication direction control switch, and the latter simply with loudspeakers adapted also to be utilized as microphones. The communication direction control switch is operable selectively to connect the loudspeaker at the master station to the input and output of the amplier and simultaneously to connect; the selected substation loudspeakers to the output and input of the amplier so that communication may be carried on between the master and substations alternately in opposite directions.

A second type of system comprises a plurality oi master stations, each provided with a loudspeaker, an amplifier, a station selector switch or switches, and a communication direction control switch normally connecting the loudspeaker to an interstation circuit for reception of calls from other stations and operable into a iirst displaced position in which the interstation line is connected to the input of the amplifier and the loudspeaker to the output for reception through the amplier, and operable also into a second displaced position in which the interstation circuit is connected to the output and the loudspeaker to the input of the amplifier for transmission through the amplifier. Systems of this type may also include substations provided with loudspeakers and switches for connecting the loudspeakers to the amplifier input when the communication control switches are in an alternate normal position, which position is the first of the two displaced positions referred to above.

A third type of system also includes a number of master stations, each provided with a loudspeaker, an amplifier, a station selector switch or switches, and a communication direction control switch. The latter normally connects the loudspeaker to an interstation circuit individual to -that station for the reception of calls and is operable into a displaced position wherein the loudspeaker is connected to the input of the amplier and the output of the amplier is connected to a selected interstation circuit individual to another station.

It is an object of the present invention to provide a new and improved intercommunicating unit which may -be used in conjunction with other similar units to provide a new and improved system, and which units and system may be operated with and include, respectively, the various types of prior art units referred to above.

Another and more specific object of the present invention is to provide a new and improved unit of the type mentioned, in which the loudspeaker is connected to both the output of the ampliiier and to an interstation circuit individual thereto for reception of calls from two diierent types of stations, and in which means are provided for enabling calls coming in over the interstation circuit readily to be heard through the loudspeaker.

Other objects and advantages of the present invention will become apparent from the ensuing description, in the course of which reference is had to the accompanying drawings, in which:

Fig. 1 is a diagrammatic representation of a portion of the system of the present invention, which portion includes two units constructed in accordance with the invention;

Fig. 2 is a diagrammatic representation of another portion of the system, including various forms of units heretofore used. Figs. 1 and 2, when placed alongside each other, represent a unified system;

Fig. 3 is a fragmentary diagrammatic representation of a modication of the units 0f Fig. l;

Fig. 4 is a view similar to Fig. 1 of a modification of the invention. When this iigure is placed alongside Fig. 3, the result is a complete system; and

Fig. 5 is a. view similar to Fig. 1 of a further modification of the invention. When this figure is placed alongside Fig. 2, the result is a complete system.

Referring now to the drawings, and more particularly to Figs. 1 and 2, the communication sys? tem illustrated therein is shown to consist of seven stations, numbered i to "l, inclusive, stations I and 2 being shown in Fig. 1 and the remaining stations in Fig, 2. Stations I and 2 have units embodying the present invention, and in order to simplify the following description, these two stations will be referred to as executive stations. Stations 3-and 4 each include y a master typev of prior art unit and will be revferred to hereinafter as sub-executive stations.

and it will be referred to hereinafter as a Isubordinate station. Station 6 is a station similar similar to station 5, having but one switch whereby it may call one of the executive stations, and station 1 is a station similar to stations 5 and 6, but having no switches for originating calls. 1

Before considering the details of the circuit arrangement and operation of the system as a whole and of the various units, it may be well brieily to describe the main elements located at each of the stations.

Station I includes an amplifier I0, a loudspeaker II' utilizable both as a microphone and as a receiver, a multi-position communication direction control switch indicated generally by the reference character I2, and two groups of station selector switches I3 and I4. In the normal and indicated position of the communication control switch I2, loudspeaker II is connected to an interstation circuit I5 for the reception of calls from other executive stations and from sub-executive stations of the type of station 4. In the normal position of the communication control switch, the loudspeaker is also connected to the output of the amplifier for reception of calls from sub-executive stations of the type of station 3 and from subordinate stations of the type of station 5. Calls from the two latter types of stations are received over an interstation circuit I6 individual to station I which is connected to the ampliiier input through a normally closed selector switch I1, a circuit I8, the communication control switch and circuits to be described in detail hereinafter. The iirst group I3 of selector switches includes also a selector switch I9 for connecting circuit Ill to an interstation circuit individual to station 3, and a selector switch 2l for connecting circuit. I8 to a circuit 22 individual to station 5. The second group i4 of selector switches includes selector switch 23 for connecting an amplifier output circuit 24 to an interstation circuit 25 individual to station 4, and selector switches 26, 2l' and 28 for connecting circuit 24 to interstation circuits 29, and 3I individual to stations 6, 1 and 2, respectively.

The unit at station 2 corresponds to that at station I. It includes an amplier 35, a loudspeaker 36 utilizable both as a microphone and as a receiver, a multi-position communication direction control switch indicated generally by the reference character 31, and two groups of station selector switches 38 and 39. In the normal and indicated position of the communication control switch, loudspeaker II is connected to the interstation circuit 3I for the reception of calls from other executive stations and from sub-executive stations of the type oi station 4. In the normal position of the communication control switch, the loudspeaker is also connected to the output of the amplifier for reception of calls from subexecutive stations of the type of station 3 and from subordinate stations of the type of stations 5 and 6. Calls from the two latter types of stations are received over an interstation circuit 40 individual to station 2, which is connected to the amplifier input through a normally closed selector switch 4I, a circuit 42, the communication control switch and circuits to be described in detail hereinafter.

The first group 38 of selector switches includes selector switches 43, 44 and 45 for connecting the circuit 42 to the interstation circuits 20, 29 and 22, individual to stations 3, 6 and I5, respectively.

The second group 39 of selector switches includes selector switches 46, 41 and 48 for connecting an amplifier output circuit 49 to interstation circuits I5, 25 and 30, individual to stations I, 4 and 1, respectively.

The apparatus at station 3 includes an amplifier 5I, a. loudspeaker 52 utilizable both as a receiver and as a microphone. and a communication direction control switch 53. In the normal and indicated position of the switch, the amplifier is operative, the loudspeaker 52 is connected to the output of the amplier, and a circuit 54 connected to all of the selector switches is connected to the input of the amplifier. The selector switches include a normally closed switch 55 for connecting circuit 54 to the interstation circuit 20 individual to station 3, and selector switches 56, 51 and 58 for connecting circuit 54 to the interstation circuits I6, 22 and 40, individual to stations I, 5 and 2. respectively.

The apparatus at station 4 includes an ampliiier 6I, a loudspeaker 62 utilizable both as a receiver and as a microphone, and a communication direction control switch 63. In the normal position of the switch the amplier is rendered inoperative and the loudspeaker 62 is connected to the interstation circuit 25 individual to station 4 for the reception of calls from other stations. In the displaced positions of the switch, the amplifier is rendered operative and the loudspeaker is connected to the input of the amplier and the output circuit 64 of the latter is connected to a selected station or stations through selector switches 65, 66, 51 and 68, individual to stations I, 6, 1 and 2, respectively.

The apparatus at station 5 includes a loudspeaker 69, utilizable both as a receiver and as a microphone, connected directly to interstation circuit 22 individual to station 5. The station also includes a selector switch 1U operable to connect the loudspeaker to interstation circuits I6, 20 and 40, individual to stations I, 3 and 2` respectively, whereby station 5 may call the enumerated stations,

The apparatus at station 6 includes a loudspeaker 1I permanently connected to interstation circuit 29 individual to station 6 and a normally open switch 12 operable to connect the loudspeaker to interstation circuit 40 individual to station 2, whereby the latter may be called by station 6.

Station 1 includes a loudspeaker 13 permanently connected to interstation circuit 30 individual to station 1.

Returning now to Fig` l and station I, the amplifier I0 may be of any suitable type having input and output connections, and it may be supplied with power through a pair of conductors 15. It is conditioned for instantaneous operation upon completion of the B supply circuit, which circuit is completed through conductors 16 and switch blade 11 forming part of the communication control switch. In the normal position of the switch, the B supply circuit is completed through a resistor 18, so that the amplier is operated at reduced B potential for the reception of calls from stations of the type of 3 and 5. The feature of rendering the amplifier normally operative with reduced B" potential is disclosed and claimed in my copending application Serial No. 364,133, iiled November 4, 1940 (now Patent No. 2,280,280, granted April 21, 1942) and assigned to the assignee of this application. When the communication control switch is operated to its uppermost position, the B" circuit I5 is connected to the loudspeaker through a potentiometer '|9, circuit 88, switch segments 8| and 82 of the communication control switch, and circuit 83. Interstation circuit I6 is connected to the amplifier input through the previously mentioned normallyclosed selector switch Il, circuit |8, switch blades 84 and 85, and the amplier input circuit 86. The output of the amplier is connected to the loudspeaker through the output circuit 8l, switch segments 88 and 89, circuit 90 including resistors 9|, and thence through the previously mentioned potentiometer 79, circuit 80, switch segments 8| and 82, and circuit 83.

Resistors 9| are utilized to prevent the secondary winding of the amplifier output trans- .former (not shown) from short-circuiting the interstation circuit I5 and loudspeaker to any substantial extent in order that calls coming in over interstation circuit I5 will be heard. Resistors 9| may have values equal to one-half the impedance oi the loudspeaker voice coil and the secondary winding-e. g., impedances of ohms as compared to 50 ohms. These resistors also serve to reduce the volume when listening and prevent excessive distortion due to the nonlinearity and rectication of the plate load of the tube feeding the output transformer.

Station is conditioned for transmitting .rnessages through the amplifier thereat when the communication control switch I2 is operated to its lowermost position. When this is done, the loudspeaker is connected to the input of the amplifier and the output of the amplifier is connected to circuits I8 and 2li. Loudspeaker Il is connected to the input of the amplifier through circuit 33, switch segments 8| and 82, and the input circuit 86. The amplifier output circuit Bl is connected to circuit I8 through switch segments 88 and 89, circuits 28 and 92, and switch blades Bil and 85. Circuit 24 is connected to 'the amplifier output circuit 8l directly by the switch segments 88 and 89.

While themiddle position of the communication control switch is its preferred normal position, the switch may be operated to its uppermost position for another normal position. 1n this other normal position, station I is conditioned for the reception of calls from other stathereinto but is returned by a spring 94 'from its lowermost to its middle position.

The apparatus at station 2 corresponds identically with that at station I and, consequently, it is not deemed necessary to describe it in detail. The corresponding circuit elements at -station 2 have, however, been indicated by adding the suiiix 2 to the various numbers.

The apparatus at station 3 includes the amplier 6| supplied with power through circuit 91 and conditioned for instantaneous operation upon completion of the B supply circuit. The B supply circuit is completed through a circuit 98 by a switch blade 99 forming part of the communication control switch 53. In the normal position of the switch, as already indicated, the B supply circuit is completed, the loudspeaker 52 is connected to the output, and the circuit 54 is connected to the input of the amplifier. The loudspeaker 52 is connected to one side of the output circuit |00 through conductor |0| and switch elements |02 and to the other side of the output circuit |00 through conductor 03, switch elements |04, conductor |05, resistor |08, and switch element |01. At the same time the resistor |08 is connected in parallel with the voice coil ofthe loudspeaker. The circuit 5t is connected to the input circuit I?? directly through switch elements |I|l and l j When the switch is operated to its lower position, loudspeaker 52 is connected to the input of the amplier, while circuit 5t is connected to the output. Loudspeaker 52 is connected to one side of the input circuit |89 throughconductor il and switch elements |02 and to the other side through conductor |03 and switch elements |88. Circuit 50 is connected directly to the output circuit |00 by switch elements H0 and III. In this position the B supply circuit is completed as before. The switch is preferably provided with a spring ||2 for returning it from its down to its middle position.

In the up position of the communication control switch 53, which may be an alternate normal position, the B supply circuit is brokenI up by switch blade 99 and the loudspeaker 52 is connected directly to circuit 54 by means of switch blades ||0 and I i. In this position, station 3 maybe called only by stations provided with amplifiers.

The amplifier 8| at station 6 is supplied with power through circuit ||5 and is conditioned for instantaneous operation upon completion of the B supply circuit I|5 by switch blade IIB. The communication control switch is normally in its intermediate position, at which time the B supply circuit is broken and loudspeaker 62 is connected to interstation circuit 25 individual to station t through circuit ill, switch blades IIS, and potentiometer H9. In both displaced positions of the communication control switch, the B supply circuit is completed and the loudspeaker connected to the ampliiier input and circuit 64 connected to the output. Loudspeaker B2 is connected to the amplifier input circuit |20 through circuit ||1 and switch blades IIB, and circuit 64 is connected to the amplier output by switch blade IZI.

It is believed that the apparatus at stations 5, 8 and l has already been described in suiicient detail, so that further amplication is not necessary and that the operation thereof will be apparent from the following description of the operation of the system as a whole. It is believed further that the operation of the units and of the systems of the present invention may be understood best by considering the modes of operation when stations oi the various types communicate with each other, and the following portion of the speciiication has been based on this assumption.

(1). Communication between stations 1 and 2 The mode oi.' communication between stations I and 2 will be considered rst when the communication control switches at the two stations are in their preferred normal positions, in'which they are indicated. When the communication `control switches are in these positions, either of the stations may call the other.

It is assumed, first, that station I calls station 2. To doI this, the operator at station I closes selector switch 28 and operates communication control switch I2 to its lowermost position. In this position the loudspeaker I I is connected to the input of amplier I and the output of the amplier is connected to circuit 24, and thence through the closed selector switch and the interstation circuit 3l individual to station 2 to loudspeaker 36 at station 2, the circuit 3I being connected to the loudspeaker through circuit 80-2, switch segments 8I-2 and 82-2, and circuit 83-2. The ampliiied output from station I is thus supplied to loudspeaker 'i speaker 5 2.

36 at station 2 and in part is dissipated in the output transformer of amplifier at station 2, but, as already pointed out, the part so dissipated is decreased by placing resistors 9I--2 between the amplier output and the potentiometer IS-2.

To respond to a call from station I, the operator at station 2 closes selector switch 46, thereby connecting output circuit 49 to interstation circuit I5 individual to station I and operating switch 31 to its lowermost position,.and the operator at station I, in order to receive, must release the communication control switch I2 thereat so that it returns to its middle position. Thus, alternate two-way communication is possible by alternatel operation of the'communication control switches I2 and 31 at stations I and 2.

In case station 2 calls station I, the foregoing operation is repeated with the operator at each station performing the operation previously performed by the other.

The alternate normal positions of the communication control switches at stations I and 2 are their uppermost positions. When the switches are in these positions, the loudspeakers at the two stations are connected only to interstation circuits. Assuming now that the communication 1 control switches are in their uppermost positions, then station I canrcall station 2 by closing selector switch 28 and operating the communication control switch thereat to its lowermost position. This connects loudspeaker II to the input of amplifier I0 and the output of the latter to loudspeaker 36 at station 2 through interstation circuit 3I individual to station 2, resistors 9I-2, circuit SII- 2, switch segments 38-2 and 89-2, circuit 93-2, switch blades 84-2 and 85-2, and circuit 83-2. To respond to a call, the 'operator at station 2 closes selector switch 46, individual to station I, and thereafter the communication control switches at the two stations are alternately operated between their middle and lowermost positions, as heretofore described.

The operation, when station 2 calls station I, corresponds to the above except that the operator at each station performs the operation previously performed by the other.

(2). Communication between station 3 and stations 1 and 2 `speaker 52 at station 3, it being remembered that with the communication control switch at the latter in its normal position, circuit 54 is connected to the input of the amplier and the output of the amplier is connected to the loud- Thereafter, the'direction of communication is controlled by the operator at station 3, the communication' control switch 53 being operated to its middle position for station 3 to receive and to its down position for station 3 to talk.

In the event the communication control switch at station 3 is in its second alternate normal position, that is, in its up position,` then the operator at station I can call station 3 by closing selector switch I 9 and operating the communication control switch I2 to its lowermost position. This connects loudspeaker II to the input of amplier Ill and the output of the latter is connected to loudspeaker 52 through interstation circuit 20 and switch blades IIII and III at station 3. The direction of communication is reversed by releasing communication control switch I2 so that it returns to its middle position.

Station 3 can call station I when the communication control switch at the latter is in its indicated normal position by closing selector switch 56 and operating communication control switch 53 to its uppermost position. Loudspeaker 52 is thus connected to the input of amplifier I 0 at station I through switch blades III) and III, circuit 54, switch 56, and interstation circuit I6. When called, the operator at station I can reverse the directionof communication by operating the communication control switch thereat to its lowermost position. Thus, communication in opposite directions is carried on under the c-ontrol of communication control (3). Communication between station 4 and stationsl and 2 Communication between station 4 and stations I and 2 is carried on in a manner similar to that between stations I and 2. For station I to call station 4, it is necessary for the operator at station I to close selector switch 23 and to operate switch I2 into its lowermost position. This connects loudspeaker II tc the input of amplifier I and the output of the latter to circuit 24, selector switch 23, lnterstation circuit 25, and thence to loudspeaker 62 at station 4 through switch blades I I8. vTo reply, the operator at station 4 closes selector switch 65 and operates the communication control switch 63 to its lowermost position, and in order for the operator at station Ito receive the reply, the communication control switch I2 thereat must be releasedto return toits middle position. .For two-way communication, it is necessary for the operators at the two stations alternately to operate the communication control switches between their lowermost and middle positions.

For the operator at station 4 to call station I, it is necessary for him to close selector switch 65 and operate switch 63 to its lowermost position, and to answer, the operator at station I must close selector switch 23 and operate the communication control switch I2 thereat.

In case the communication control switch I2 at station I is left in its uppermost normal position, station 4 may call station I in the same manner. Thereafter, however, station I has to operate switch I2 between its middle and lowermost positions after receiving an initial call.

4). Communication between station 5 and stations 1 and 2 and station 3 Station I can call station 5 by closing selector switch 2I and operating communication control switch I2 to its lowermost position. This connects loudspeaker II to the input of the amplier and loudspeaker 69 to the output of the amplifier through inter-station circuit 922 and the selector switch 2|. To receive from station 4, the communication control switch I2 is released to its middle position.

Station 5 can call station I by operation of the selector switch 1D to complete a circuit from the loudspeaker to interstation circuit I6. This interstation circuit is connected to the input of the amplifier through the normally closed selector switch I1. circuit I8, switch blades 84 and 85, and circuit 86. To respond, the operator at station I preferably closes selector switch 2l and thereafter operates the communication control switch between its middle and lowermost positions. When station 5 calls station I, communication between the two stations may be carried on over the interstation circuit I6 individual to station I or with this circuit connected in parallel with the interstation circuit 22 individual to station 5, which vcircuit is connected in this manner by closure of selector switch 2-I at station I.

Communication between stations 2 and 5 is carried on in the same manner as between stations I and 5, except, of course, for the operation of the proper selector switches, and when station 5 calls station 2 by operation of selector switch 10 to connect loudspeaker 69 to interstation circuit 40 individual to station 2.

Station 5 can also call station 3 when the communication control switch 53 at the latter is in its indicated normal position. To call station 3, the

operator at station 5 moves selector switch 10 to connect loudspeaker 69 to interstation circuit 20 individual to station 3. This intersection circuit is connected to the input of amplier 6I and the output of this amplifier is connected to loudspeaker 52.l To answer a call, the operator at station 3 may, if he desires, close selector switch 51 individual tostation 5 so that the operator at station 5 may, if he desires, return selector switch l1I) to its normal oli' position. Thereafter, the dlrection of communication is controlled by the operator at station 3, the communication control switch being operated alternately between 'its middle and lowermost positions.

(5). Communication between station 6 and stations 1 and 2 and station 4 Station 6 can call station 2 when the communication control switch at the latter is in its indicated' normal position by closing selector switch 12. This connects loudspeaker 1I to interstation circuit 40, individiual to station 2, which it may be recalled is connected to the input of ampliiier 35. To answer, the operator at station 2 may close selector switch 44 individual to station 6, so that the operator at station 6 may, if he desires, open switch 12. Thereafter,

communication between .the two stations is car- V ried on by alternate operation of communication control switch 31 at station 2 between its middle and lowermost positions. Stations I and 4 may transmit to, but not receive from, station 6. In order for stations I and 4 to be placed in communication with station 6, it is necessary that the proper selector switches at these two stations be closed. For station I to Communication between stationl 7 and stations 1 and 2 and station 4 Stations I, 2 and 4 may transmit to, but not receive from station 1. To transmit to station 1, the operators at any of stations I, 2 and 4 simply close the proper selector switches, that is, selector switch 21 at station I, selector switch 48 at station 2, and selector switch 21 at station 4.

In Fig. 3 there is illustrated an arrangement whereby stations I and 2 may be placed in com-l munication .with each other by operation of the proper selector switch at the calling station. The

arrangement has been illustrated in conjunction with a portion of the apparatus at station I. The modication consists in connecting circuit I 5, which is individual to station I, to circuit 24 which is connected to the output of ampliiier III at station I when the communication control switch is in its lowermost position. This connection is made by jumpers |23 and |24. Similarjumpers may be provided at station 2 and also at stations similar to station 4. Then when the called station selector switch is closed at the calling station, the two stations are conditioned for twoway communication by alternate operation of the communication control switches thereat between their middle and lowermost positions.

Assume, for instance, that station I desires to communicate with station 2. Then, selector switch 28 at station I is closed. To call station 2, the operator operates the-communication control switch to its lowermost position, thereby to connect loudspeaker II to the input of the amplier and to connect the output of the ampliier,

to circuit 24, selector switch 28, and interstation circuit 3l. Interstation circuit 3| is connected `to loudspeaker 36 through the circuit 80-2,

switch segments 8I-2 and 82-2, and circuit 83-2. To answer, the operator at station 2 operates communication control switch 31 to its lowermost position after the operator at station I releases communication control switch I2 to return the latter to its middle position. Loudspeaker 35 is thus connected to the input of the ampliiier 35 and the output of the latter is connected to interstation circuit 3| through jumpers corresponding to `iumpers |23 and |24 at station 2, and interstation circuit 3| is connected to loudspeaker at station I` through selector switch 28, circuit 24, jumpers |23uand |24, the potentiometer 18, circuit 80, switch segments 8| and 82, and circuit 83. This circuit may be utilized where secrecy of communication between stations is not necessary.

A modiedform oi' unit which may be used in conjunction with other similar units or with the various types oi' prior art units referred to above is illustrated diagrammatically in Fig. 4, to which reference will now be had. In Fig. 4, stations I and 2 are illustrated as having identical equip- A ment, which equipment corresponds in part to that illustrated in Fig. 1. The corresponding parts have been indicated by like reference characters.

Referring now more particularly to the equipment at station it will be noted that the communication direction control switch I2 diilers from that shown in Fig. 1 and that the station has been provided also with a group selector switch indicated generally by the reference character I3I.

The communication direction control switch I2, like that of the embodiment of Fig. 1, has two normal positions, although its preferred normal position is the middle position in which it is illus- |38 leading to switch blades |32 and |38 which are connected to the loudspeaker.

The resistors I 48 perform the same function as performed by the resistors 8l in the embodiment of Fig. 1, i. e., they prevent the output transformer of the ampliiier from short-circuiting signals sent to station over the interstation circuit I5.

'I'he alternative normal position otthe communication direction control switch at station I is its uppermost position in which the ampliiier I0 is rendered inoperative by disconnection of its B supply. In this position oi' the switch the loudspeaker I is connected directly to circuits 5 and I8 for the reception of calls from other stations in the system. The loudspeaker is connected to circuit I5 through conductors 83. u

. switch is operated to its lowermost position, the

trated. The group selector switch I3I normally occupies the position in which it is indicated. In this position it connects station I for the reception of calls from various outlying stations and in its displaced position it conditions the station for reception of calls from other similar stations or from sub-executive stations of the character of. station 4 having access to interstation circuit I5.

'I'he communication direction control switch I2 includes the amplifier B supply controlling switch 11 and a plurality of circuit controlling switch blades |32 to |31, inclusive. In the indicated position of the switch, the loudspeaker is connected to. interstation circuit I5 for the reception of calls from other executive stations and from sub-executive stations oi the type of station 4. 'I'his connection extends through conductors 83, switch blades |32 and I 35 and conductors |39. At the same time the station is conditioned for the reception of calls from sub-executive stations of the type of station 3 and from certain of the subordinate stations as the interstation circuit I8 through which these stations may call station I is connected tothe input of amplifier I0 and the output of the amplifier is connected to loudspeaker I I. Interstation circuit I8 is con- -nected to the input of the ampliiier through a pair of 'switch blades |40 forming part of the previously referred to group selector switch I3I, a pair of conductors I 4| and 42 leading to switch blades |33 and |38, respectively, and theamplliler input conductors 88. The output of the amplier is connected to loudspeaker I through the output conductors 81, switch blades |34 and |31, conductors |43 and |44, a second pair of switch blades |45 forming part of the group selector switch I3I. a pair of resistors |48 and conductors loudspeaker is connected to the input of the ampliiier and the output oi.' the ampliiier is con- *i nected either to circuit I8 or circuit 24, depending upon the position of the group selector switch I 3|. In the indicated position of the latter, the output of the ampliiier is connected to circuit I8 for the transmission of messages to stations connected to interstation circuits I6, 20 and 22 (that is, to stations 3 and 5) through conductors 81, switch blades |34 and |31 in their lowermost positions, the pair of branch conductors |40 (which are also connected to conductors |43 and |44), switch blades |33 and |38 in their lowermost positions, the pair of conductors I4| and |42 and switch blades |40. At this time the output of the amplifier is also connected to interstation circuit I5 through conductors |43 and |44, the switch blades |45 and resistors |48;v but since interstation circuit I5 is normally not connected to the amplifiers or loudspeakers at any of the other stations, this connection has no deleterious effect on the operation.

When the group selector switch |3I is operatedto its displaced position, circuit I8 is disconnected from the communication switch and circuit 24 is connected to the conductors |43 and |44 directly through the switch blades |45. The latter also break the circuit I5 through resistors |48 so that the output of the amplifier goes only lwith the sumx 2 and further description thereof is not deemed necessary in view of the following description of the operation of the system as a whole. 'I'he system as a whole is disclosed in Figs. 4 and 2, and more particularly when the former is placed to the left of the latter.

(1) Communication between stations 1 and 2 The mode of communication between stations and 2 will be considered nrst when the communication direction control switches are in their aeaaeio indicated preferred normal positions, at which time either of the stations may cali the other. It is assumed that station I calls station 2. To do this, the operator at station Imoves group selector switch I3| to its displaced position to connect switches |45 to circuit 24 and closes station selector switch 28 and operates switch I2 to its lowermost position. In this position the loudspeaker II is connected to the input of amplier I0, and the-output of the latter is connected to circuii-I 24 and thence through switch 28 and interstation circuit 3|, individual to station 2, to loudspeaker 36 at station 2, the circuit 3| being connected to the loudspeaker -36 through circuit I39-2, switch blades |32-2 and ISS-f2, and circuit 83-2. The ampliiler output from station I is thus supplied to loudspeaker 36 at station 2 and in part is dissipated in the output transformer of ampliner 35, but, as already pointed out, the part so dissipated is decreased by placing resistors |46-2 between the amplifier output and circuit 3|.

To respond to a call from station I, the operal tor at station 2 closes the station selector switch 46, thereby connecting circuit 49 'to interstation circuit I5 individual to station I, operating group station circuit 2|, and thence through' amplier tion is possible by alternate operation of the communication control switches I2 and 31 at stations I and 2 after the respective station selector switches have been closed and the group selector switches |3| operated to their displaced positions.

When the communication direction control switches at stations I and 2 are in their upper or alternate normal positions, then station I can call station 2 in the manner described above, i. e., by operating switch |3|` to its displaced position, closing selector switch 28 and operating switch I2 to its lowermost position. Loudspeaker II is thus connected to the input of amplifier l0, and the output of the latter is connected'to loudyno' speaker 36 at station 2 through interstation circuit 3|, conductors |39-2, switch blades |32-2 and |35-2 in their uppermost positions and conductors 8 3-2L At this time ampliiler 35 is inoperative and both its input and output circuits are broken. To respond, the operator at station 2 operates switch I 3|-2 to its displaced position, closes selector switch 46 and operates switch 31 to its lowermost position. To receive the response, the operator at station releases switch I2 allowing it to return to its middle position and thereafter, as previously, alternate two-way communication is carried on by operation of switches I2 and 31 between middle and lowermost positions.

In case station 2 calls station I, the foregoing operations are repeated, with the operator at each station performing the operation previously performed by the other.

(2). communication between station s and 'stations 1 and 2 A Inasmuch as stations and 2 are identical, it

' of communication is reversed by 5I to loudspeaker52 at station 3. In this position of switch I2. the amplier I0 at station I is rendered inoperative. Thercafter, the direction of communication is controlled by the operator at station 3, the communication direction control switch 53 being operated between its middle and lowermost positions to condition station 3 forreception and transmission, respectively.

In the event the communication control switch y at station 3 is in its second alternate normal position, .that is, in its up position, then the operator at station can call station 3 by closing station selector switch I9 and operating switch I2 to its lowermost position. This connects loudspeaker IIto the input of amplier I0 and the output of the latter is connected to loudspeaker 52 through interstation circuit 20 and switch blades III) and atstation 3. YThe direction releasing switch |2 to return it'to its middle position.

Station 3 can call station when the communication control switch at the latter is in its indicated normal position by closing selector switch 56 and operating communication vcontrol switch 53 to its uppermost position. Loudspeaker 52 is thus connected to the input of ampliiler I0 at station I through interstation circuit I6 and the normally closed switch I1,l switches |40 and l the input circuit 86.- The output of the ampliiier I0 is connected to loudspeaker through a circuit previously described and including the output conductors 81, resistors |46 and circuit |39. When called, the operator at station |4 can reversethe direction of communication by operating the communication control switch thereat to its lowermost position, thereby reversing the connections of the interstation circuit and loudspeaker to the amplier.

Station 3 can also call station when the communication control switch at the latter is in its second normal position, that is, in its uppermost position. Under these conditions, station I is called by closure of selector switch 56 and operation of communication control switch 53 at station 3 to its lowermost position. To receive an answer from station I, the communication control switch at station 3 must be returned to its middle position.

In the event the selector switch |3| is in its displaced position, then station 3, as well as any other stationsconnected to or adapted to be connected to interstation circuit I6, cannot call` stationl because the circuit I8 is disconnected by switches |40 from the communication control switch.

(3). Communication between station 4 vand stations 1 and 2 station 4, it is necessary for the operator at the former to close selector switch 23 and operate switch |3| "to its displaced position and switch I2 into its lowermost position. Inasmuch as loudspeaker 62 at station 4 is normally connected to interstation circuit 25, it may be seen that when position, conditioning the loudspeaker 52 thereat.

the switches at station I are operated as indicated, then station I can call station 2 through amplie'r I0 at the former. To reply, the operator at station 4 closes selector switch 65 and operates communication control switch 63 to its lowermost position, and in order for the operator at station I to receive the reply, the communication control'switch thereat must be released to return to its middle position. For two-way communication, it is thereafter necessary for the operators at the two stations alternately to operate the communication control switches between their lowermost and middle positions, although it is possible for the operator at station I to operate the communication control switch thereat alternately between its uppermost and lowermost positions.

For the operator at station 4 to call station I, it is necessary for him to close selector switch 65 and operate switch 63 to its lowermost positions, and to answer, the operator at station I must close selector switch 23% and operate the communication control switch thereat.

In case the communication control switch at station I is left in its uppermost or alternate normal position, station 4 may call station I in the same manner. Thereafter, however, station I preferably operates switch I2 between its midle and lowermost positions for two-way communication. although. as stated above. it is Dossible to operate switch I2 alternately between its 4uppermost and lowermost positions.

(4). Communication between station 5 stations 1 and 2 Station I can call station 5 by closing station selector switch 2| and operating communication control switch I2 to its lowermost position. This connects loudspeaker II to the input of the amplier and loudspeaker 69 to the output of the amplifier through interstation circuit 22, se-

and

lectorfswitch 2|, and switch blades I 40. To re-A l ceive from station 4, the communication control switch is released to return to its middle position Station 5 can call station I when switches |3I and I2 at station I are in their indicated positions by operation of selector switch to complete a circuit from the loudspeaker to interstation circuit I6, which, it may be remembered,

is individual to station I. This interstation circuit is connected to the input of amplier I0 through a circuit including circuit I8, switch blades |40, and switch blades `|33 and |36. To

respond, the operator at station I preferably Cil closure of selector switch 12. 'Ihis connects loudspeaker 1I to interstation circuit 4| individual to station 2, which, it may be recalled, is connected to the input of ampliiler 35. To answer, the operator at station 2 may close selector switch 44 individual to station 6 so that the operator at station 6 may, if he desires, open switch 12. Thereafter, communication between the two stations is carried on by alternate operation of switch 31 at station 2 between its middle and lowermost positions.

Station I may transmit to, but not receive from, station 6, inasmuch as no provision is made for station 6 to call station I. Station 6, however, being connected to its interstation circuit 29, may be called by station I upon closure of station selector switch 26 at the latter and upon operation of selector switch |3| to its displaced position and of communication control switch I2 to its lowermost position.

(6). Communication between station 7 and stations 1 and 2 Stations I and 2 may transmit to, but not receive from, station 1. To transmit, the operators at stations I and 2 simply close the proper selector switches, that is, selector switch 21 at station I and selector switch 48 at station 2, and operate the selector switches I3| to their displaced positions and the communication control switches to their lowermost positions.

From the foregoing it may be noted that the modes of communication between stations 5 and 3 and between 4 and 6 and 1 have not been described. The reason for this is that they correspond to those previously described.

A further modified form of unit which may be used in conjunction with other similar units or with various types of prior art units is illuscarried on in the same manner as between stations I and 5, except, of course, for operation of the proper selector switches at the two stations.

(5). Communication between station 6 and stations 1 and 2 trated in Fig. 5. In this figure stations I and 2 are illustrated as having identical equipment, which equipment corresponds in part to that illustrated in Fig. 1. The corresponding parts have been indicated by like reference characters.

Referring more particularly to the equipment at station I, it may be noted that it differs from the previously described embodiments in that two communication direction c'ontrol switches |5| and |52 are provided. The iirst of these is utilized for communication between station I and stations connected to group I3 of station selector switches and the latter for communication between station I and stations connected to group I4 of station selector switches. 'I'he switches are of the three-position type and are both normally in their uppermost positions, in which they are indicated. Switch |5| may, if desired, be utilized with its middle position as an alternative normal position. Both switches are returned from their lowermost positions to their middle positions by springs 94.

In the indicated normal positions of the switches the loudspeaker II at station I is connected for reception from other stations provided with ampliiiers, it being connected to the interstation circuit I6 individual to station I through the normally closed station selector switch I1 and circuit I8, and also to the other interstation circuit I5 individual to station I. Circuit I8 is connected to the loudspeaker through a pair of switch blades |53 forming part of switch |5I, a pair of conductors |54, a second pair of switch blades |55 also forming part*l of switch I5I, a pair of conductors |56, a pair of branched conductors |51, a pair of switch blades |58 forming of branched conductors |59, a pair of switch blades |60 forming part of switch |5I, a. pair of conductors |6I, a pair of switch .blades |62 forming part of switch |52, the previously mentioned conductors |51, switch blades |58 and circuit 83. In the indicated positions oifswitches II and |52 both the input and output circuits 86 and 81, respectivelyl of the amplifier are open.4

Switches I5I and |52 are both `operable from their` uppermost positions to middle and lowermost positions. When switch |5I is operated to its middle position, circuit I8 is connected to the input of the ampliiier (which is normally operative) and loudspeaker II to the output. Circuit I8 is connected to the input through switch blades |53 in their middle positions, a pair of branched conductors |63 and the input circuit 86. Loudspeaker II is connected to the output cf the amplier through circuit 83, switch blades |58, conductors |5| and |56, switch blades |55 in their middle positions and .the pair `of conductors |64 which are connected to ampliiier output circuit 86. Conductors |64 are each provided with resistors |64' .corresponding to resistors ,9| and |46 of the previously described embodiments.

When switch I5I is operated to its lowermost position, circuit I8 is connected to the output of the amplier and loudspeaker II to the input. Circuit I8 is connected to the outputl through switch blades I 53, and the pair of conductors |65. Loudspeaker II is connected to the amplier input through circuit 83, switch blades |58, circuits |51 and |56, switch blades |55 in their lowermost positions, the pair of conductors |63 and the input circuit 86.

When switch |52 is operated to its middle position with switch I5I in its uppermost position, then circuit I5 is connected to loudspeaker II and when operated to its lowermost position loudspeaker II is connected to `the input of the amplifier and the output is connected to circuit 34 and the group It of station selector switches. In the middle position of the switch, circuit I5 is connected to the loudspeaker II through the pair of conductors |59, switch blades ISI), conductors IGI, switch blades |62, conductors |65, switch blades |58 and circuit 83. In the lowermost position loudspeaker II is connected to the input of the amplifier through circuit 83 and switch blades |58 and input circuit 86. In this position of switch |52, circuit 2li is connected to the output of the amplifier through a pair of switch blades |58 forming part of switch |52 and a pair of conductors |69 connected to the out-Y put circuit 8l.

The apparatus at station 2 corresponds with that at station I, the corresponding elements being indicated by like reference characters with the suhx 2. The system as a whole is disclosed in Figs. 5 and 2, and more particularly when the former is placed to the left of the latter.

(1). Communication between stationsg 1 and 2 The mode of communication between stations I and 2 will be considered rst when the communication direction control switches are in their indicated normal positions, at which time either station may call the other. It is assumed station I calls station 2. The operator at station closes station selector switch 28 and operates switch I 52 to its lowermost position. In this position loudspeaker I| is connected to the input of ampliiler I0 and the output of the latter is connected to circuit 24 and thence through switch 28 and interstation circuit 3| individual to station 2, to the loudspeaker 36-at station 2, circuit 3| being connected to .the loudspeaker through circuit I59-2, switch blades I'60-2, circuit I6I-- 2, `switch blades 'IGZ-'2, circuit |5I`-2, 'switch y blades |58-'2 and circuit 83-2. The amplifier output at station 2 is open circuitedat .this time.

To'respond to the call, the operator at station 2 closes station selector switch 46, thereby con- Y necting circuit 49 to interstation circuit I5 linditoits lowermost position. The operator at staof conductors |59 and |59--2.

vi'dual tov station I and operates switch |52-2 tion I, in order to receive, must release switch |52 to return it to its middle position wherein loudspeaker II is connected to circuit I5 through a circuit that remains the same-as-described above except conductors |66 are substitutedfor conductors |51, thus disconnecting circuit I8 fromy loudspeaker II. Thereafter, communication in opposite directions is carried on by alternate operation of switches I5I and I52-2 between their middle and lowermost positions.

When the switches I5I and I5I--2 are in their alternative normal positions, communication between stations I and 2 is carried on in the manner described above, the -onl-y difference being that circuits I5 and 3| are connected to switch blades |68 and I60-2 through the other branches Circuits I8 and 42, however, are connected to the inputs of the amplifiers I8 and 35, respectively, so that 'to avoid interruptions by calls from stations connected to circuits I8 and 42, the selector switches of groups- (2). Communication between station 3 and stations 1 and 2 Inasmuch as stations I and 2 are identical, it

is believed that it will be suflicient to describe communication between stations I and 3. Station I can call station 3 when the communication control switch at the latter is in its indicated position, conditioning the loudspeaker at station 3 for reception through ampliiier 5|, by closing station selector switch I8 to connect circuit I8 to interstation circuit 20 individual to station 3. This connects loudspeaker II to interstation circuit 20 and thence through amplifier 5I to loudspeaker 52 at station 3. Thereafter, the direction of communication is controlled by the operator at station 3, communication direction control switch 53 being operated between its middle and lowermost positions to condition station 3 for reception and transmission, respectively.

In the event communication direction control switch at station 3 is in its second alternative normal position that is, in its up position, then the operator at station I can call station 3 by closing station selector switch I9 and operating switch I 5I to its lowermost position. This connects loudspeaker II to the input of amplifier IIJ and the output of the latter is connected to loudspeaker 52 through interstation circuit 20 and switch blades III) and I II at station 3. The direction of communication is reversed by releaslector switch B and operating communication control switch 53 to its iowermost position. Loudspeaker 52 is thus connected to the input oi' amplifier 5| and the output of the latter is connected to loudspeaker II through interstation circuit I6 and the normally closed switch l1 at station I. The direction of communication is controlled by the operator ai; station 3 by moving switch 53 between its middle and iowermost positions. Y i

Station 3 can also call station I when the communication control switch I5| at the latter is in its middle position, at which time loudspeaker I is connected to the output of ampliiier I0 through resistors 64' and circuit I8 is connected to the input of amplifier I0. AThe operator at station 3 merely operates the communication control switch 33 to its uppermost position, thus connect-` ing loudspeaker 52 to interstation circuit I6 through station selector switch 56 corresponding to station I. The direction of communication is controlled by the operator at station i.

(3). Communicationbetween station 4 and stations 1 and 2 Communication betweenstation 4 and stations I and 2 is carriedon in-a manner similar to that between stations i and 2. For station I to call station it is necessary for the operator at the former to close selector switch 23 and operate communication direction control switch |52 to its iowermost position. This connects loudspeaker ii to the input of the ampliiier and the output of the amplifier is connected to circuit 24 and thence through interstation circuit 25 to loudspeaker 62 at station 4. To reply, the operator at station 4 closes station selector switch 65 and operates communication direction control switch 63 to either its iowermost or uppermost position. In order for the operator at station I to receive the reply, the switch |52 thereat is returned toits middle position. Thus, for two-way communication, it is necessary for the'operators at the two stations alternately to operate the switches between their viowermost and middle positions. l

For the operator at station 4 to call station I, it is necessary for him to close selector switch 85 and operate switch 53 to its iowermost position and to answer. The operator at station I must close selector switch and operat`e`the communication control switch thereat.

. In the event switch |5| at station I is left in its alternate normal position to condition that station for reception of calls from stations not provided with ampliers, then station 4 can call station I in the manner described above. l At this time interstation circuit I5 is connected in parallel to the loudspeaker and to the output trans- Y former of amplifier I0. The connection to the latter is through resistors |64', so that only part ofthe energy is dissipated in the output transformer.

selection switch 2| and operating communication direction control switch |5| to its iowermost po- I sition. This connects loud speaker ||l to the input of the amplifier and loudspeaker 69 at station'S to the output of the amplifier through interstation circuit 22. To receive from station 4,

the communication control switch |5| is released to return to its middle position.

aseaeic `Station l, which is not provided with an ampliner, can call station I only when switch |5| at the latter is in its alternate normal position wherein circuit I8 is connected to the input ci' the ampliner and loudspeaker II is connected to the output of the amplifier. Direction of com- (5). Communication between station 6 and Statns 1 and 2 Station 2 can calistation S by closing selector switch 44 and operating switch |5|2 to its lowermost position. To receive from station 3, the switch |5|2 is released to return it to its middle position.

Station B can call station 2 when switch i5I-2 at the latter is in its middle position by the operator at station 5 closing switch 12.

Station I may transmit to but not receive from station 8,V inasmuch as no provision is made for station 6 to call station I. Station 6, however, being connected to interstation circuit 29, may be called by station I upon closure of station selector 26 at the latter and upon 'operation of switch |52 to its'lowermost position.

(6) Communication between station 7 and stations 1 and 2 Stations and 2 may transmit to but'not receive from station 1. To transmit, the operators at the two stations simply close the proper selector switches and operate communication control switches |52 and |52-2 to theirV iowermost positions.

The modes of communication between stations 5 and 3 and between 4 and 6 and 'I have not been described, as they correspond to those previously described.

Although the present invention has been disclosed in connection with the specific details of preferred embodiments thereof, it should be understood the details are. not intended to be limitative of the invention except in so far as set f orth in the accompanying claims.

Having thus described vmy invention, what I claim as new and desire to secure by Letters Patent of the United States is:

1'. In an intercommunicating system, the combination including, a plurality of stations each having a loudspeaker utilizable both as a microphone and a receiver, an amplifier, and communication direction control switch means, a plurality of communication circuits between stations, each of said stations having one of said circuits as its individual circuit for reception from other stations, each of said stations also having a. transmission circuit and station selector switch means for connecting the station to the individual circuits of other stations, means including circuits controlled by said communication direction control switch means at the respective stations for connecting the loudspeaker to the ampliier output and to the circuit `individual to -the station, and resistance means in the amplifier output circuit between the output and the point of con'nection of the circuit. f

2. In a multiple station intercommunication system, the combination including; one or more stations of a rst type including a loudspeaker utilizable both as a microphone and receiver, an amplifier, an interstation circuit, and a communication direction control switch operable in arst position to connect the loudspeaker to the interstation circuit, in a second position to connect the loudspeaker to the amplier input and the interstationcircuit to the output of the amplifier, and in a third position to reverse the connections of the interstation circuit and loudspeaker to the amplier; one or more stations of a second type Vincluding a loudspeaker utilizable both as a microphone and receiver, an amplifier a rst interstation circuit individual thereto leading to other stations, and a communication diloudspeaker to said individual rection control switch operablein one position to connect the loudspeaker to the circuit individual thereto and in a second position to connect the loudspeaker to the amplifier input and the amplifier output to interstation circuits individual to other stations; and one or more stations of a third type having a rst interstation circuit connected to interstation circuits of the first type of station, second and third interstation circuits leading to other similar stations and stations of the second type, said second circuit being individual to the station, and communication direction controlling switch means operable to connect said loudspeaker to said iirst and second interstation circuits, whereby stations of said nectable to interstation circuits of stations of the first type, and means including said communication direction controllin'g switch means for connecting the loudspeaker to both said one circuit and said third circuit, whereby said station may be called by stations of either type.

4. In a multiple station intercommunication system, the combination including; one or more stations of a first type including a loudspeaker utilizable both as a microphone and receiver, an amplier, an interstation circuit, and a communication direction control switch operable in a rst position to connect the loudspeaker to the interstation circuit, in a second position to connect the loudspeaker to the amplifier input and the interstation circuit to the output of the amplifier and in a third position to reverse the connections of the interstation circuit and loudspeaker to the amplier; one or more stations of a second type including a loudspeaker utilizable both as a microphone and receiver, an amplifier, a iirst interstation circuit individual thereto leading to other stations, and a communication direction control switch operable in one position to connect the loudspeaker to the circuit individual thereto and in a second position to connect the loudspeaker to the amplifier input and the amplifier output to interstation circuit individual to other stations; and one or more stations of a third type Y having a rst interstation circuit connected to interstation circuits of the first type of station, second and third interstation circuits leading to other similar stations and stations'of the second type, said second circuit being individual to the station, and communication controlling switch means operable (l) to connect said loudspeaker to said first and second interstation circuits, (2)

to connect said first interstation circuit to the input of the amplier and said loudspeaker to the output of the amplifier and to said second interstation circuit, and (3) to connect said loudspeaker to the amplier input and the amplifier output to said first or third interstation circuits.

5. In an intercommunicating system, the combination including, a. plurality of stations each having a loudspeaker utilizable both as a microphone and a receiver, an ampliner, and a single multiple position communication direction control switch, a plurality of communication circuits between stations, each of said stations having one of said circuits as its individual circuit for recepttion from other stations, each of said stations also the second type, a tr having station selector switch means for connecting the station to the individual circuits of other stations, means including circuits controlled by said communication direction control switches at vthe respective stations for connecting the loudspeaker to the amplifier output and to the circuit individual to .the station, and resistance means in the amplifier output circuit between the output and the-point of connection of the loudspeaker to said individual circuit.

6. In an intercommunicating system, the combination including, a plurality of stations of a iirst type having interstationcircuits individual thereto, a plurality of stations of a second type each including an amplifier, a loudspeaker utilizable both as a microphone and a receiver, a multiple position communication direction control switch, a first circuit adapted to be connected to said interstation circuits, a second circuit individual thereto and l ading to other stations of smission circuit, circuits individual to other stations of the second type, selector switch` means for connecting the transmission circuit to the circuits individual to said other stations, and means including circuits controlled by said control switch for connecting 1) the rst circuit to the ampliiier input and the loudspeaker to .the amplifier output and to said second circuit, in one position of said control switch, (2) the loudspeaker .to both said first and second circuits, in a second position of said control switch, and (3) the loudspeaker to the ampli,- iier input and the amplifier output to said first circuit and said transmission circuit, in a third position of said switch.

7. In an intercommunicating system, the comdividual thereto and leading to other stations of the second type, said second circuit including resistance means, a transmission circuit,l circuits individual to other stations of the second type, selector switch means for connecting the transmission circuit to the circuits individual to said other stations, and means including circuits controlled by said control switch for connecting (1) the first circuit to the amplifier input andthe loudspeaker to said second circuit and to the ampliner output through said resistance means, in one position oi' said control switch, (2) the loudspeaker to both said iirst and second circuits, in a second position of said control switch, and (3) the loudspeaker to the ampliner input and the amplifier-output to said nrst circuit and said transmission circuit, in a third position of sai switch. l 8. In an intercommunicating system, a combination including a plurality. of stations each having loudspeakers utilizable both as a microphone and a receiver, an amplifier, and communication direction control switch means, a plurality of communication circuits between stations, each of said stations having one of said circuits as its individual' circuit for reception from other stations, each of said stations also having a transmission circuit and station selector switch means for connecting the transmis'- sion circuit to the .individual circuits of f the other stations, a jumper circuit connecting the circuit individual to the station to said transmission circuit, and means including circuits controlled by said communication direction control switch means at the respective stations for connecting the loudspeaker to the amplifier output and to the circuit individual to the station.

9. In an intercommunicating system, the combination including, a plurality of stations of a rst type. a plurality of stations of a second type, each of the latter having a loudspeaker utilizable both as a microphoneiand a receiver, a circuit extending to stations of the first type utilizable for both reception and transmission, a circuit individual thereto utilizable for reception and extending to other similar stations, a circuit adapted to be utilized for transmission, station selector switch means for connecting said transmission circuit to circuits individual to other stations, an amplier, a communication direction first type. a plurality of stations of a secondtype, each of the latter having a loudspeaker utilizable both as a microphone and a receiver, a circuit extending to stations of the iirst type utilizable for both reception and transmission, a circuit individual thereto utilizable for reception and extending to other similar stations, a circuit adapted to be utilized for transmission, station selector switch means for connecting said circuit to circuits individual to other stations, an amplifier, a multiple position communication direction control switch, resistance means, a twoposition selector switch, and circuits controlled .by said control switch and selector switch so constructed and arranged that in one position of said selector switch the control switch is operable (l) in one position to connect saidloudspeaker to said iirstI mentioned circuit and to the circuit individual to the station, -(2) in a second vposition to connect said loudspeaker to the circuit individual to the station and to the amplifier output through said resistance means and to connect said first mentioned circuit` to the amplifier input, and (3) in a third position to connect the loudspeaker to the amplifier input and the amplifier output to said iirst circuit; and

that in the other position of said selector switch the control switch is operable in said first two positions to connect said loudspeaker to the circontrol switch, and means including' selectortype, each of the latter having a loudspeaker a circuit extending to stations of the iirst type utilizable for both reception and transmission, a circuit individual thereto utilizable for reception and extending to other similar stations, a circuit adapted to be utilized for transmission, station selector switch means for connecting said vcircuit to circuits individual to otherl stations,

an ampliiier, a multiple position communication direction control switch, and means including atwo-position selector switch and circuits controlled thereby and by said control switch for connecting, in one position of said selector switch, the circuit extending to stations of the rst type to the amplier input, the loudspeaker to the amplifier output and to the circuit-individual to said station, and for connecting, in the otherposition of -said selector switch, said transmission circuit to the ampliiier output and breaking said circuit extending to stations vof the first type.

11. In an intercommunicating system. the combination including, a plurality or stations of a -utilizable both as a microphone and agreceiver,

cuit individual to the station and in said third position to connect said loudspeaker to the amplierinput and the amplifier output tosaid transmission circuit.

12.,An intercommunicating system, including ond type.

13. An intercommunicating system, including in combination, one or more stations of a. first type, a plurality of stations of a second type. a Vcommunication circuit utilizable for both receptionandtransmission between stations aLl-.he second type and stations of the iirst type, and

a pairofv communication-circuits between sta-v tions of the'second type. one utilizable for recep- 1 tion andthe other for transmission, each of thestationsof the second type having a loudspeaker vutilizable both as a k.microphone and a receiver,

an amplifier, a pair of multiple position communication direction control Switches, and circuits controlled thereby, said switches and circuits being so constructed and arranged that when both switchesoccupy one position, the loudspeaker is connected to said first communication circuit-and to said reception circuit, one of said switches being operable tofanother position to connect the loudspeaker to the amplifier input vand the ampliiier output to said first circuit, and theother of said switches being operable to anotherv position to connect the loudspeaker to the amplifier I input andthe amplifier output to said transmission circuit.

14. An intercommunicating system, including in combination, one or more stations of a first type, a plurality of stations of a second type,

and 'a communication circuit utilizable for both reception and transmission between stations of associe of multiple position communication direction control switches, and circuits controlled thereby, said switches and circuits being so constructed and arranged that when both switches occupy one position, the loudspeaker is connected to said rst communication circuit and to said reception circuit, each of said switches being operable to another position to connect the loudspeaker to the amplier input and the amplifier output to either said iirst circuit or said transmission circuit, one of said Switches being operable to a third position wherein said loudspeaker is connected to said reception circuit and to the amplier output through said resistance means and said rst circuit is connected to the amplii'ler input, and the other of said switches being operable to a third position wherein said reception circuit is connected -to said loudspeaker.

15. A unit for use in intercommunicating system, including in combination a loudspeaker utilizable both as a microphone and a receiver, an amplifier, and communication direction control switch means, an individual circuit adapted for reception from other units, selector switch means adapted to connect the unit to the individual circuits of other units, means including circuits controlled by said communication direction control switch means for connecting the loudspeaker to the amplifier output and to said individual circuit, and resistance means in the amplier output circuit between the output and the point of connection of the loudspeaker to said individual circuit.

16. A unit for use in an intercommunicating system, including in combination, an ampliiier, a loudspeaker utilizable both as a microphone and a receiver, communication direction control switch means, a pair of interstation circuits individual thereto, one of said circuits being utilizable for reception and the other for transmission, a third circuit utilizable for both reception and transmission, and means including communication direction controlling switch means for connecting the loudspeaker to said one circuit and said third circuit.

17. A unit for use in an intercommunioating system, including in combination, a loudspeaker utilizable both as a microphone and a receiver, an amplifier, and a single multiple position communication direction control switch, a reception circuit individual thereto, station selector switch means adapted to connect the unit to the individual circuits of other units, means including circuits controlled by said communication directoin control switch for connecting the loudspeaker to the amplifier output and to the circuit individual to the unit, and resistance means in the amplifier output circuit between the output and the point of connection of the loudspeaker to said individual circuit.

18. A unit for use in an intercommunicating system, including in combination, an amplifier, a loudspeaker utilizable both as a microphone and a receiver, a multiple position communication direction control switch, a first circuit adapted to be utilized for transmission and reception, a second circuit individual to the unit and adapted to be used for reception, a transmission circuit, and means including circuits controlled by said control switch for connecting (1) the first circuit to the amplier input and the loudspeaker to the amplier output and to said second circuit, in one position of said control switch, (2) the loudspeaker to both said iirst and second circuits, in a second position of said control switch, and (3) the loudspeaker to the ampliiier input and the amplier output to said irst circuit and said transmission circuit, in a third position of said switch.

19. A unit for use in an intercommunicatins system, including in combination, an amplier, a loudspeaker utilizable both as a microphone and a receiver, a multiple position communication direction control switch, a rst circuit adapted to be utilized for both transmission and reception, a second circuit individual to the unit and adapted to be utilized for reception, said circuit including resistance means, a transmission circuit, and means including circuits controlled by said control switch for connecting (1) the iirst circuit to the ampliiier input and the loudspeaker to said second circuit and to the amplier output through said resistance means, in one position of said control switch, (2) the loudspeaker to both said rst and second circuits, in a second position of said control switch, and (3) the loudspeaker to the ampliler input and the ampliier output to said first circuit and said transmission circuit, in a third position of said switch.

20. A unit for use in an intercommunicating system, including in combination, a loudspeaker utilizable both as amicrophone and a. receiver, an amplifier and communication direction control switch means, a circuit individual to the unit, a. transmission circuit and unit selector switch means for ,connecting the transmission circuit to the circuits leading to the other units, a jumper circuit connecting the circuit individual to the unit to said transmission circuit, and means including circuits controlled by said communication direction control switch means for connecting the loudspeaker to the amplifier output and to the circuit individual to the unit.

21. A unit for use in an intercommunicating system, including in combination, a loudspeaker utilizable both as a microphone and a receiver, a circuit adapted to be utilized for both reception and transmission, a circuit individual to the unit utilizable for reception and adapted to be extended to other similar units, a circuit adapted to be utilized for transmission, station selector switch means for connecting said transmission circuit to circuits individual to other units, an ampliner, a communication direction control switch, and means including selector switch means and circuits controlled thereby for connecting the rst mentioned circuit to the amplier input and the loudspeaker to the arnplier output.

22. A unit for use in an intercommunicating system, including in combination, a loudspeaker utilizable both as a microphone and a receiver, a circuit utilizable for both reception and transmission, a circuit individual to said unit utilizable for reception, a circuit adapted to be utilized for transmission, unit selector switch meanss for connecting said circuit to circuits individual to other stations, an ampliiier, a multiple position communication direction control switch, and means including a two-position selector switch and circuits controlled thereby and by said control switch for connecting, in one position of said selector switch, the first mentioned circuit to the amplifier input, the loudspeaker to the amplifier output and to the circuit individual to said unit, and for connecting, in the other position oi' said selector switch, said transmission circuit to the amplifier output and breaking said first mentioned circuit.

23. A unit for use in an intercommunicating system, including in combination, a iirst communication circuit adapted to be used for reception and transmission, a second circuit adapted to be used for reception, a third circuit adapted to be used for transmission, and a pair of communication direction controlling switches, one for controlling communication over said first circuit and the other for controlling communication over said second and third circuits.

24. A unit for use in an intercommunicating system, including in combination, a communication circuit utilizable for both reception and transmission, a pair of communication circuits, one utilizable for reception and the other for transmission, a loudspeaker utilizable both as a microphone and a receiver, an amplifier, a pair of multiple position communication direction control switches, and circuits controlled thereby, said switches and circuits being so constructed and arranged that when both switches occupy one position, the loudspeaker is connected to said first communication circuit and to said reception circuit, one of said switches being operable to another position to connect the loudspeaker to the ampliiier input and the amplifier output to said first circuit, and the other of said switches being operable to another position to connect the loudspeaker to the amplier input and the amplifier output to said transmission circuit.

25. A unit for use in an intercommunicating system, including in combination, a communication circuit utilizable for both reception and transmission, and a pair of communication circuits, one utilizable for reception and the other for transmission, a loudspeaker utilizable both as a microphone and a receiver, an amplifier, resistance means, a pair of multiple position communication direction control switches, and circuits controlled thereby, said switches and circuits being so constructed and arranged that when both switches occupy one position, the loudspeaker is connected to said first communication circuit and to said reception circuit, each of said switches being operable to another position to connect the loudspeaker to the amplifier input and the ampliiler output to either said first circuit or said transmission circuit, one of said switches being operable to a third position wherein said loudspeaker is connected to said reception circuit and to the amplifier output through said resistance means and said ilrst circuit is connected tothe ampliiier input, and the other of said switches being operable to a third position wherein said reception circuit is connected to said loudspeaker.

26. A unit for use in an intercommunicating system, including in combination, a loud speaker utilizable both as a microphone and a receiver, a circuit utilizable for both reception and transmission, a circuit individual to said unit utilizable for reception, a circuit adapted to be utilized for transmission, unit selector switch means for connecting said circuit to circuits individual to other stations, an amplier, a multiple position communication direction control switch, resistance means, a two-position selector switch, and circuits controlled by said control switch and selector switch so constructed and arranged that in one position of said selector switch the control switch is operable (1) in one position to connect said loud speaker to said iirst mentioned circuit and to the circuit individual to the unit, 2) in a second position to connect said loud speaker to the circuit individual to the unit and to the amplifier output through said resistance means and to connect said first mentioned circuit to the amplifier input, and (3) in a third position to connect the loud speaker to the ampliiier input and the amplifier output to said iirst circuit; and that in the other position of said selector switch the control switch is operable in said first two positions to connect said ,loud speaker to the circuit individual to the unit and in said third position to connect the loud speaker to the amplifier input and the amplifier output to said transmission circuit.

RICHARD H. CAMPBELL. 

